Method of recovering hydrogen fluoride from hydrocarbon mixtures



FROM HYDROCARBON MIXTURES Filed Jan. 1, 1944 Patented June 29, 1948 METHQD F BECOMING FLUURIDE FROM HYDBOCABBQN MIX- TUBES Lucien H. vantraln. loner, Tex., allignor to Phillips Petroleum Company, a corporation of Delaware Application Januar! l, 1344, Serial No. 516,672

6 Claims. (Cl. 2Mb-083.4)

This invention relates to the distillation oi' mixtures of hydrogen uoride and hydrocarbons. In a specic embodiment the invention relates to the recovery of hydrogen iuoride from admixture with hydrocarbon material containing lowboiling paraffin hydrocarbons. The invention in a. specific modification relates to the operation of an azeotropic fractionation wherein a low-boiling parafiin-hydrogen iiuorlde azeotrope is recovered overhead with the production oi' a hydrogen fluoride-free bottom product.

Hydrogen fluoride has recently come into prominence as a very important catalyst for numerous organic reactions. For example, it is used as a catalyst in the conversion of hydrocarbons by alkylation, isomerization. reconstruction, cracking, cyclization and/or aromatization. It is also used as a reactant in the production of alkyl uorides. Liquid hydrogen iluoride has also been found useful as a refining agent or selective solvent in the removal of certain impurities from saturated hydrocarbons.

Perhaps the most important industrial process at the present time involving the use oi hydrogen iluoride is the alkylation of low-boiling parailinic hydrocarbons, particularly lsobutane, with alkylating agents, particularly oleilns such as propylene and butylenes, to form normally liquid high octane number paraiiins suitable for use in aviation fuels. In such alkylation processes the reactants are intimately contacted in liquid phase with liquid concentrated hydroiluorie acid, and reaction eilluents are passed to a settling zone wherein a liquid hydrocarbon phase and a liquid acid phase are separated. The acid phase is largely recycled to the reaction and a portion thereof may be subjected to puriiicatlon, as by distillation for the removal of water and acidsoluble oils, before being re-lntroduced as a catalyst into the process. The hydrocarbon phase is ordinarily introduced at an intermediate point into a fractionating tower provided with kettle heating and reflux cooling, from which tower an overhead fraction is recovered comprising all the hydrogen fluoride together with at least suiilcient light hydrocarbons to form azeotropes therewith. Inasmuch as a large excess o! the low-boiling paraiiln reactant. such as isobutane, is maintained in the alkylation reaction mixture, and some propane is usually also present, there is adequate light hydrocarbon in the feed to the azeotrope tower to allow complete separation oi hydrogen uoride overhead. The overhead product may -be subjected to separate cooling and condensation and passed to a separate settling zone for separation of acid phase and hydrocarbon phase. The acid phase is returned to the reaction. while the hydrocarbon phase is pumped to the top of the azeotropc tower to provide reflux. A large volume of light hydrocarbons must thus'be continually condensed and revaporized to provide sumcient cooling. 'I'he reiiux accumulator and pump required for this operation are of course subject to corrosion by the acid.

In the operations lust described it is necessary to provide a substantial amount of cooling in the top oi' the fractionator for the production of redux. This is done either by internal coolins coils within the iractionator. which are subject to well-known limitations and objections. or by external condensation of a portion of the overhead product and pumping resulting condensate to the top of the iractionator as in the method described. which is ordinarily preferred. Sufficient cooling must be provided to remove a substantial portion of the heat imparted to the system by the reboller at the bottom of the column. Such reboiling and refiuxing operations are now well known to the art. Furthermore, the i'ractionator is operated at a relatively high pressure due to the low-boiling nature of the overhead product.

It is an object o! this invention to provide an improved process for the distillation oi' hydrogen fluoride-containing mixtures.

Another object is to recover hydrogen fluoride from admixture with hydrocarbons.

A further object is to improve the operation of a fractionation system in which a minimum-boiling azeotropic mixture of hydrogen uoride with low-boiling paramnic bvdrocarbon material is produced in an overhead product.

Yet another object is to provide redux for such a system in a novel and advantageous manner.

Another obiect is to reduce the amount oi cooling required in such a system.

Another object is to reduce the pressure in such a system.

A further object is to reduce the equipment needed for such a system.

A yet further object is to provide such a system in which the amount of equipment in contact with acid is reduced.

Another object is to increase the capacity oi' a fractlonator.

Still another object is to recover a hydrocarbon fraction substantially free of hydrogen fluoride from a mixture containing low-boiling hydrocarbons and hydrogen fluoride.

A further object is to provide an improved 3 method tor recovering hydrogen fluoride catalyst for re-use in a reaction zone. and to recover hydrocarbon material free from hydrogen fluoride, in a process for the conversion of hydrocarbons. particularly in an alkylation process.

Other objects and advantages oi' the invention will be apparent, to one skilled in the art. from the accompanying disclosure and description.

I have now discovered an improved manner of carrying out fractionations of the nature described. By employing the principles of my invention the complete recovery of hydrogen nuoride overhead is possible without the necessity of providing the conventional reflux, while still producing the desired HF-iree bottom product.

In this improved manner of operating the azeotropic distillaticm. the cooling ordinarily provided in the top of the aaeotrope tower may be entirely dispensed with. Nor is it necessary to provide an arrangement for separate condensation and recovery oi' overhead product for re-use as reluxing medium. In addition to the savings in equipment. which is an important item at the present time, the amount of equipment in contact with acid, and hence subject to corrosion. is reduced. A given fractionator is also enabled to handle a larger load, that is produce more bottom product oi a given purity. l l

The improved operation is obtained in a very simple manner by introducing the liquid hydrocarbons phase. from which acid has been settled but which still contains dissolved acid, as feed to the fractionator at the top of the fractionator rather than at an intermediate point as is conventional, coupled with removing overhead vapors and returning the same to a point in the system ahead of the fractionator, preferably to the acid settler. This liquid feed is normally obtainable at substantially atmospheric temperatures, and since the. fractionator is readily and usually operated at elevated temperatures, the feed itself provides all the cooling that is necessary within the fractionator. Even when the'feed is at somewhat elevated temperatures, the fractionator is easily operated at sumciently higher temperature that the feed acts as reflux. In some cases in fact, the feed is heated .somewhat before introduction into the fractionator. It willaccordingly be seen that the liquid feed containing dissolved hydrogen iiuoride as well as low-boiling unreacted hydrocarbons and higher-boiling alkylate acts as reiluxing medium for the 4azleotrope tower. The 'overhead vapors carrying the hydrogen fluoride are condensed and returned to the acid settler together with the reactor eiuents, rather than to a separate settler as heretofore, so that carrying over of heavier hydrocarbons. which occurs to a limited extent in this method of operation,` introducesl no` problems, for these heavier hydrocarbons are merely returned again to the fractionator. .Such an operation as this settler. top of the "azeo tower, condenser. and back to the settler. Acid dissolved in the hydrocarbon phase passes once through this circuit and upon returning to the settler in the overhead condensate does not redissolve in the hydrocarbon phase, which is already saturated with HF, but settles out and is recovered with the acid phase. The total hydrocarbon portion' of the reactor eilluent, except that small part which is dissolved in the acid phase, passes into the fractionator and out as kettle product. The net eil'ect is that the hydrocarbon phase 'from the acid settler is stripped only of dissolved HF. By the practice of my invention not only are considerable equipment and cooling costs avoided but an extremely smooth operation of the fractionator is obtained. This is due in part to the fact that only one stream need be controlled as it enters the fractionator. By operating the fractionator as a stripper in accordance with the invention, the capacity of the fractionator is increased. and it may be operated at a lower pressure. or at higher temperatures, which in any case allows greater throughput.

The invention may perhaps be more adequately understood by reference to the accompanying drawing and description thereof. The drawing represents somewhat diagrammatically one preferred arrangement of apparatus elements, and flow of materials therethrough, in which the process of the invention may be practiced. While the elements essential to an understanding oi' the invention are shown in the drawing, it will be appreciated that various auxiliary pieces oi' equipment may be provided by one skilled in the art. It will also be appreciated that various modiilcations may be made without departing from the spirit and scope of the invention.

In the drawing a reaction zone is represented diagrammatically by the rectangle i0. In a preferred operation this reactor is used in carrying out the alkylation of a low-boiling parafn, preferably isobutane, with one or more low-boiling is impossible in ordinary fractional distillations `because of contamination of overhead product olens, such as a mixture of butenes. The isoparaiiln may be introduced by line I2 while the oleiln is introduced by line il. Make-up liquid hydrogen fluoride catalyst is introduced through line iB. The bulk of the catalyst is recycled to the reactor from the bottom of settling tank ill via lines 20 and 22. In some cases it is desirable to incorporate a minor amount of boron fluoride -with the liquid hydrogen uoride as disclosed in the copending application of Frey, Serial No. 467,954.

Methods of effecting the desired alkylation reaction wlll not be described here in detail inasmuch as they form no part of the present inven- -tion and are known to the art. Such methods are disclosed, for example, in U. S. Patent 2,322,800 of Frederick E. Frey, Freys application Serial No. 424,204 and the aforesaid application of Frey, Serial No. 467,954. While an alkylation reaction is disclosed specifically in describing the invention. it is to be understood that reactions other than alkylation may be carried out in reactor lil. For example, the isomerizatlon of saturated hydrocarbons in the presence of hydrogen iiuoride as a catalyst may be carried out in reactor Ill. Furthermore, a combination of HF-catalyzed alkylation and isomerlzation reactions may be effected in reactor Ill in one or more stages. it will be appreciated that my invention may be applied to eilluents from any of such processes or others known to the art involving the conversion or treatment of hydrocarbon materials in which an eiuuent stream containing hydrogen fluoride aussie and low-,boiling hydrocarbons is obtained. The apparatus comprising reactor Il may accordingly be varied to suit the particular process and will comprise one or more reaction zones and may in addition comprise much auxiliary apparatus which need not be shown or discussed here in detail.

Considering the case in which isobutane is alkylated with butylenes in reactor I0, liquid concentrated hydrofluoric acid and liquid hydrocarbon reactants under pressure.' are agitated together to produce a temporary emulsion of hydrocarbon and acid phases and give ready access of isobutane to the acid phase wherein most of the reaction takes place. The emulsion is vigorously circulated to distribute the olefin reactant in low concentration and thus discourage polymerization and permit a maximum of alkylation. A severalfold molar excess at least of isobutane over olehn is maintained to minimize realkylation of primary alkylate. Normal paraillns act as diluents and impede access of isobutane to the catalyst and are preferably kept at low concentration. Actually,

due to the impracticability of preparing absolutely pure feed stocks and possibly due also to side reactions, some normal butane and some propane are ordinarily present, along with traces of lighter gases. A reaction temperature of 'l5 to 115 F. gives good results and can be maintained by water cooling to take up exothermic heat of reaction; refrigeration is not necessary. Reaction time is less than one hour, and ordinarily 10 to 15 minutes is adequate. With continued use the acid acquires acid-soluble organic contaminants which are removed by distillation; the titratable acidity of the catalyst phase is usually maintained at 85 to 90 per cent.

Eniuents from the reactor zone i0 contain unconverted low-boiling hydrocarbons including propane and a large excess of isobutane, together with higher-boiling paraillnic hydrocarbons produced by alkylatlon reaction and hydrogen fluoride catalyst. Such effluents are continuously Withdrawn via lines 24 and 2i and passed to settling tank IB wherein a phase separation is readily obtained. In case the conversion carried out in reactor I0 is at a temperature above that allowing separation of the effluents into the liquid phases, suitable cooling means (not shown) may be provided in line 24 or line 26 to effect the desired phase separation and bring the mixture to the preferred temperature range. The acid phase is withdrawn from settler I8 vla line as heretofore mentioned and returned by pump 2| to the reactor. A portion of this acid ls usually withdrawn via line 20 and passed to purlcation means not shown, after which it is reintroduced along with make-up acid through line IB. From settling tank I8 the upper (hydrocarbon) phase, which contains small amounts of hydrogen uoride dissolved therein, is passed via line 30 into surge tank 32. Small amounts of undissolved acid may drop out in tank 32 and be recovered through line 34. Pop-oil' lines 29 and 3i are provided at the tops of tanks l il and 32, respectively, for release oi' small amounts of light gases which may accumulate therein. In a typical operation the tanks are held under 100 and 60 pounds gage fpressure, respectively. The liquid hydrocarbon phase containing dissolved HF yis withdrawn `through line 36 by means of pump n and passed via line Il) and/or line 4| into a high point of fractionator 42, preferably being introduced upon the top tray of the fractionator. This liquid feed is ordinarily obtained from surge d tank Il etV substantially atmospheric temperatureoroniyslightlyaboveandneednotbefurther cooled before being introduced into tower I2. In fact. in order to increase the capacity of the fractionator. the feed stream may be heated somewhat by heater 3l.

In exeotrope tower Il a continuous fractionation is carried out whereby all of the dissolved hydrogen nuoride is stripped from the feed and withdrawn in the overhead product via line Il along with at least suilicient propane. isobutane. and/or other light hydrocarbons to form an aseotropic mixture therewith. Propane and lighter gases may comprise a substantial proportion of the light hydrocarbon material taken oif in line I4. the remainder being isobutane and heavier. including some vaporized alkylate. 'Ihe lowbolling fraction in line u is passed to condenser I8 and the condensate passed therefrom vla line IB to accumulator l1. Uncondensed gases may be periodically or continuously withdrawn through line Il. Pressure in accumulator l1 is normally held at about 12B-160 pounds. or a little lower than the fractionator presusre. Liquid passes via line li to settling tank il in admixture with the reactor eilluents. or may be passed to tank 32 if desired.

From the bottom of fractionator l2 a liquid stream is passed by means of pump Il through line 52 into reboiler means Il wherein suilicient heat is imparted by a heat source such as fire or steam to carry out the fractionation in tower 42. This reboiler is preferably an externally heated unit as shown. but may comprise heating coils placed within the bottom of tower 42 in known manner. In the arrangement shown heated liquid is returned to the lower portion of the fractionator through tlie line Il. A kettle product essentially free from hydrogen uoride is withdrawn through line Il. This product comprises the normally liquid alkylate as well as inert hydrocarbons and excess isobutane, and corresponds essentially to the hydrocarbon content of the reactor eiiiuents except for that dissolved in the acid phase in settler il. The HF- free kettle product is passed to further fractionation means (not shown) for the recovery and recycle of isobutane through line I2, and recovery of the desired alkylate. Ordinarily this kettle product is subjected lto a defiuorlnation treatment prior to such fractionation.

As an example of the actual operation of an alkylation plant in accordance with my invention, the following data are presented. It will be appreciated that these data are merely illustrative and are not to be construed as being unduly limiting the invention. A combined hydrocarbon feed including fresh reactants plus recycled isobutane is passed into the reactors at F. at a rate of 732 `barrels per hour. The perature of this feed may upon occasion vary from about 75 to about 100 F.. and the quantity may range from 600 to 900 barrels per hour. depending upon availability of feed stocks. Recycle, regenerated. and makeup acid enters at similar temperatures (80 F. in this instance) and similar rates (732 barrels per hour) so that a 1:1 volume ratio of hydrocarbon to acid is used. Total emuents from the reactors is passed to settler i8 at a temperature of 80 F. Hydrocarbon liquid in the quantity of 820 barrels per hour is pumped from the settlers through line I0 and heater Il, wherein it is raised to -130" 1".. in this case F., at which temperature it enters the top of the azeotrope column l2. This stream may vary from 650 to 1000 barrels per hour with the previously mentioned range of feed rates. Column 42 is a 'l foot diameter. 2D plate fractionator, and is operated with a kettle temperature of 183 1i'. (180-190 Il'. ordinary range), at 164 pounds per square inch gage pressure (ranging from 160-160 pounds) and an overhead vapor temperature of 147 F. (M5-150 F. range) The overhead vapors upon condensation amount to 85 to 100 barrels per hour, of which 5 to 15 barrels per hour is HF. In the specific operation here described, 82 barrels per hour overhead is produced. of which 12 barrels is HF. The kettle product of 1" barrels per hour is free from HF.

It is interesting to note that the above operation represents an appreciable overload on the column in comparison with design and ordinarily used throughput rates. However, the practice o! the present invention is an important factor in enabling the column to handle this load and still produce a hydrogen fluoride-free kettle product.

I claim:

1. In a process for the production of a normally liquid paramnic hydrocarbon material by the alkylation of low-boiling alkylatable paraiiinic hydrocarbons with an alkylating agent in the presence of la hydrogen-iluoride-containing a1- kylation catalyst, the improved method oi' recovering hydrogen fluoride for re-use in the process and also recovering said normally liquid paraiilnic hydrocarbon material substantially free from hydrogen fluoride which comprises passing material eilluent from said alkylation and containing a liquid hydrogen uoride phase and a liquid hydrocarbon phase including unconverted low-boil- 'ing alkylatable parafilns to a phase separating means, passing also to said phase separating means a low-boiling fraction comprising hydrogen fluoride and low-boiling paraiflns obtained as hereinafter described, recovering liquid hydrogen fluoride phase from said phase separating means and returning same to said alkylation, passing liquid hydrocarbon phase containing dissolved hydrogen fluoride from said phase separating means to the top of a fractional distillation means as feed and as substantially the sole redux. supplying heat to the bottom oi' said fractional distillation means to eiect fractionation therein. recovering irom the top of said fractional distillation means a low-boiling fraction containing essentially all of said dissolved hydrogen fluoride together with at least suiiicient low-boiling paraiiins to form a minimum-boiling azeotropic mixture with said hydrogen iluoride and passing same to said phase separating means as described, and recovering from the bottom of said fractional distillation means a substantially hydrogen fluoride-free hydrocarbon material comprising said normally liquid parafllnic hydrocarbon material produced in said alkylation.

2. The process of claim l, wherein said lowboiling alkylatable paramns comprise isobutane.

3. The process of claim 1, wherein said lowboiling allnviatable paramns comprise isobutane, and wherein minor amounts of propane are present in said liquid hydrocarbon phase and in said low-boiling fraction.

4. In a process for the production of a normally liquid paramnic hydrocarbon material by the alkylation of low-boiling alkylatable paramnic hydrocarbons with an alkylating agent in the presence of a hydrogen fluoride-containing alkylation catalyst, the improved method for re- 8 l, covering hydrogen `fluoride for re-use in the process and also for recovering said normally liquid paramnic hydrocarbon material substantially free from hydrogen fluoride which comprises passing a resulting eiiiuent from said alkylation to a separating means in which a liquid hydrogen nuoriderich phase and a liquid hydrocarbon-rich phase are formed. recycling at least a portion of said hydrogen fluoride-rich phase to said alkylation, passing said\liquid hydrocarbon-rich phase containing dissolved hydrogen fluoride into a high point in a fractional distillation sone at a temperature sufllciently low that said liquid phase acts as reflux in said zone, said liquid hydrocarbon-rich phase being the sole redux provided to said zone, separating from said fractional distillation a low-boiling vaporous fraction containing a low-boiling paraiiln hydrocarbon and hydrogen fluoride, cooling and condensing said low-bolling fraction without further fractionation, circulating the resulting condensate from the aforesaid condensation to said` separation means whereby the hydrogen fluoride in said low-boiling fraction is returned to said alkylation and separating also from said fractional distillation a higher-boiling hydrocarbon fraction substantially free from hydrogen fluoride and containing normally liquid parailinic hydrocarbon material produced in said alkylation.

5. In a process for reacting paramn hydrocarbons in the presence of hydrogen fluoride, the improvement which comprises passing eiiluents directly from a reaction zone, in which a lowboiling paraffin is reacted in the presence of a catalystcomprising hydrogen fluoride, to separating means under conditions such that liquid hydrogen fluoride separates as a separate phase from a liquid hydrocarbon phase, returning at least a portion of said liquid hydrogen fluoride phase back to said reaction zone, passing said liquid hydrocarbon phase containing dissolved hydrogen fluoride to a high point in a fractional distillation zone as feed and as substantially the sole reux for said zone, stripping from said feed in said fractional distillation zone a low-boiling fraction containing hydrogen fluoride and a lowboiling paramn, and returning said low-boiling fraction to said separating means whereby the hydrogen fluoride in said low-boiling fraction is returned to said reaction zone.

6. In a process for the production of a normally liquid paramnic hydrocarbon material by the alkylation of isobutane with an alkylating agent in the presence of a hydrogen fluoride-containing alkylation catalyst, the improved method for recovering hydrogen fiuoride for re-use in the process and also for recovering said normally liquid parafilnic hydrocarbon material substantially free from hydrogen fluoride which comprises passing a resulting eilluent from said alkylation in the liquid phase to a separation zone wherein a liquid hydrocarbon-rich phase and a liquid hydrogen fluoride-rich phase are formed, passing said hydrocarbon-rich phase containing dissolved hydrogen fluoride at a temperature between about and about 130 F. as substantially the sole feed into a high point in a fractional distillation zone, said mixture being the sole reflux provided to said zone, maintaining a kettle temperature between about 180 and about 190 F. and an overload vapor temperature between about and about 150 F., maintaining a pressure within said distillation zone between about and about 180 poundsper square inch gage, separating from said fractional distillation a lowboiling vaporous overhead fraction comprising essentially all oi the hydrogen iluoride in said mixture entering said fractional distillation zone together with isobutane, separating also from said fractional distillation a liquid hydrocarbon traction essentially free from hydrogen fluoride containing nornxally liquid paraiiinic hydrocarbon material as a product oi the process, condensing said low-boiling overhead fraction without further fractionation to i'orm a liquid hydrogen 11u0- ride-rich phase and a liquid hydrocarbon-rich phase, passing substantially all ot the resulting condensate of the aforesaid condensation to said separation zone and recycling said hydrogen fluoride-rich phase to said alkyiation.

LUCIEN H. VAUTRAIN.

REFERENCES CITED The following references are oi record in the ille of this patent:

tion." second edition (1930), pages 101 and 102. Continental Plant: "The Rener": volume 21, January 1942; pages 51-56 and 58.

Robinson: "Elements of Fractional Distillation." second edition, published 1930 by McGrawn Hill Book Co., 370 Seventh Ave., New York, N. Y.

Copy in Div. 25. pages 170 and 171.

Certificate of Correction Pate-nt No. 2,444,316.

June 29, i948.

LUCIEN H. VAUTRAIN It is hereby certified that errors appear in the Cprinted specication of the above numbered atent requiring correction as follows:

p perature read temperature; column 8, line 71, claim 6, for

read pressure; line 61 for olumn 6, line 24, for presusre the word overload read overhead; and that the said Letters Patent should be read with these corrections therein that the same may conform the Patent Office.

to the record of the case in Signed and sealed this 14th day of September, A. D. 1948.

THOMAS F. MURPHY,

Assistant Umnmiuoner of Patents.

boiling vaporous overhead fraction comprising essentially all oi the hydrogen iluoride in said mixture entering said fractional distillation zone together with isobutane, separating also from said fractional distillation a liquid hydrocarbon traction essentially free from hydrogen fluoride containing nornxally liquid paraiiinic hydrocarbon material as a product oi the process, condensing said low-boiling overhead fraction without further fractionation to i'orm a liquid hydrogen 11u0- ride-rich phase and a liquid hydrocarbon-rich phase, passing substantially all ot the resulting condensate of the aforesaid condensation to said separation zone and recycling said hydrogen fluoride-rich phase to said alkyiation.

LUCIEN H. VAUTRAIN.

REFERENCES CITED The following references are oi record in the ille of this patent:

tion." second edition (1930), pages 101 and 102. Continental Plant: "The Rener": volume 21, January 1942; pages 51-56 and 58.

Robinson: "Elements of Fractional Distillation." second edition, published 1930 by McGrawn Hill Book Co., 370 Seventh Ave., New York, N. Y.

Copy in Div. 25. pages 170 and 171.

Certificate of Correction Pate-nt No. 2,444,316.

June 29, i948.

LUCIEN H. VAUTRAIN It is hereby certified that errors appear in the Cprinted specication of the above numbered atent requiring correction as follows:

p perature read temperature; column 8, line 71, claim 6, for

read pressure; line 61 for olumn 6, line 24, for presusre the word overload read overhead; and that the said Letters Patent should be read with these corrections therein that the same may conform the Patent Office.

to the record of the case in Signed and sealed this 14th day of September, A. D. 1948.

THOMAS F. MURPHY,

Assistant Umnmiuoner of Patents. 

